This invention relates to a method and device for effecting registration for a copying apparatus having a magnification ratio varying device, wherein a photosensitive member in motion is exposed to an optical image of an original by slit exposure to form an electrostatic latent image thereon, by varying the original scanning velocity in accordance with the magnification ratio selected.
Nowadays electrophotographic copying apparatus equipped with magnification ratio varying devices are becoming popular. The term "magnification ratio" as used herein, refers to the ratio of the size of a duplicate produced from an original by electrophotographic copying, to that of the original. For example, when the magnification ratio is 1:.sqroot.2 a duplicate will have a size which is twice as large as that of its original; when it is 1:1, a duplicate will be equal in size to its original; and when it is 1:1/.sqroot.2 a duplicate will have a size which is one half as large as that of its original. In copying apparatus of the aforementioned type, it is necessary to effect registration of the forward end of the image of an original which is projected by a light on the photosensitive member or of the image of an original formed on the photosensitive member with the leading end of a photosensitive sheet or a transfer-printing sheet which is in motion, when copying of the original is carried out. Particularly when restriction is placed on the position in which an electrostatic latent image is formed on the photosensitive member, such as when the photosensitive member is in drum form and has wound on its periphery a photosensitive sheet which has a gap, it is essential that copying be performed by synchronizing the movement of the photosensitive member with the operation of exposing the photosensitive member to an optical image of an original and by bringing the forward end of an image formed on the photosensitive member into registration with the leading end of a transfer-printing sheet which is delivered to the transfer-printing position, in case a copying apparatus of the aforesaid type having a magnification ratio varying device is used. A change in the magnification ratio by means of a magnification ratio varying device makes it necessary to change the travelling speed of the photosensitive member or the original scanning speed. However, the structural arrangement of a copying apparatus makes it difficult to change the speed at which the photosensitive member travels. Thus it is usual practice to change the original scanning speed in accordance with a change in the magnification ratio.
A change in the original scanning speed which is necessitated by a change in the magnification ratio may cause mismatching in place of the forward end of the image of an original on the photosensitive member and the leading end of a copy sheet.